Subscapularis – Functional Anatomy

The anatomy of the subscapularis muscle is more complex than at first glance. For example, it has multiple sections and a variable attachment.

The subscapularis is a thick, fan-shaped muscle on the underside of the shoulder blade. By far, it is the largest and strongest rotator cuff muscle. Also, it is the largest shoulder muscle. A bursa separates it from the serratus anterior.

Origin

• subscapular fossa

Insertion

• lesser and greater tubercle of the humerus

Function

• internal rotation of the humerus
• stabilization of the humeral head

Innervation

• upper and lower subscapular nerves, C5-6

Attachment Details

The triangular-shaped bellies merged into a thick band that crosses the glenohumeral joint. As it crosses, a bursa separates it from the joint. It attaches firmly to the lesser tubercle. Studies vary, but most agree that the tendon continues across the bicipital groove to the greater tubercle. Of course, this assists in securing the bicipital tendon in the groove.

In fact, this study indicates that the intact subscapularis tendon is critical to the stability of the bicipital tendon in the groove. The subscapularis is structurally complex. The subscapularis and coracobrachialis restrict and create pain in the windup of pitching. Subscapularis weaves under the short head of the biceps and over the tendon of the short head.

Functional Considerations

Subscapularis has similar attachments to the teres major. Likewise, the trigger points of the lower bellies of the subscapularis also produce pain that is similar to the teres major. They both create pain when raising and externally rotating the arm. Teres major creates pain in the lower ranges. On the other hand, subscapularis creates pain in the higher ranges, especially when externally rotated.

Studies also show that there are usually tears in other rotator cuff tendons when this tendon is torn.

Subscapularis can be the primary cause of a frozen shoulder.

Anomalies, Etc.

This study of the subscapularis anatomy involved 190 specimens (380 sides). It showed that 10 of the axilla had an accessory muscle that extended from the scapula’s lateral border to the insertion of the subscapularis.

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